This application claims the priority of German application 198 37 098.9, filed Aug. 17, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for operating and a valve drive for a multicylinder internal combustion engine of the type having first and second groups of cylinders which are selectively operable.
A method according to the species for operating a multicylinder internal combustion engine is known from German Patent Document No. DE 196 0 4 737 A1. This internal combustion engine has two groups of cylinders, one of which is constantly operated and the second is operated by cutting it in and out. To operate this engine, the second cylinder group is cut out in a lower full load range and the first cylinder group is operated between zero and full load. In an upper total range, the second cylinder group is cut in and operated between zero and full load. The first cylinder group is constantly operated at full load in this upper load range. A method of this kind for operating a multicylinder internal combustion engine has the disadvantage that completely separate intake systems and intake system controls are required for the two groups of cylinders. Therefore, two separate control and regulating units and two mass airflow meters and airflow sensors connected with them are required as well.
A valve drive of an internal combustion engine is also known from German Patent Document No. DE 196 06 054 A1 that is operated with a device for changing the valve phases and with switchable lift transfer elements. As a result of the switchable lift transfer elements, the valve lift of the associated charge-changing valves can be operated with a long or short lift regardless of the valve opening phase that has been set. With a valve drive of this kind, the engine can be operated as a function of rpm (engine speed revolutions per minute) and load in various operating modes with optimum fuel consumption and emission values in each case.
On the other hand, a goal of the invention is to improve the method according to the species for operating a multicylinder internal combustion engine and the valve drive of a multicylinder engine so that an additional reduction of fuel consumption, especially at idle and under low loads, can be achieved at low structural and control-engineering cost.
This goal is achieved according to preferred embodiments of the invention by providing that at least one of the selectively operable groups of cylinders has a valve lift control operable as a function of load and/or rpm. In arrangements of the engine where the first cylinder group in an engine with a first constantly operated group of cylinders and a second group of cylinders that can be cut in and out independently of the first group are operated with different valve lift values, in both a load range with the second cylinder group cut out and in a load range with the second cylinder group cut in, in the lower part of the each of these load ranges a considerable reduction of fuel consumption is achieved by operation with a shorter valve lift. Operation of this kind has the advantage that because on the shorter valve lift in the lower load range in each case there is a significant reduction of friction and a considerable dethrottling of the intake process. Especially in the idle range, with the second group of cylinders cut out, a higher degree of smooth running of the engine can simultaneously be guaranteed. A method of this kind can be employed at only relatively low cost in the entire intake system since in particular it is not necessary to divide the intake system between the two differently operated groups of cylinders.
If the group of cylinders that can be cut in and out in a valve drive according to the species is designed so that the valve lift in each case is different and in the cut-out state of the cylinders the valve lift of the intake valves is zero or minimal, by switching the valve lift of the other cylinder group between a medium lift and a long lift, a considerable saving of fuel can be achieved as well. Especially in the lower full load range, by cutting out the second group of cylinders and operating the first group of cylinders with a short valve lift, considerable improvements in friction are achieved.
If the engine is operated with the cylinder group either cut out or constantly cut in, in the lower range of the associated load ranges with a short valve lift in the constantly operated cylinder group, considerable fuel consumption advantages can be realized especially by reducing friction. By reducing the valve lift in the lower load range in each case, an improved dethrottling is also possible on the intake side of the engine.
If the engine, with the second cylinder group either cut out and/or constantly cut in, is operated with a long valve lift in the first cylinder group, a greater degree of filling of the cylinders can be achieved in the upper levels of the associated load ranges in each case, so that significant advantages regarding power and torque are achieved with the second cylinder group either cut in or cut out.
Particularly in the respective partial load range of the constantly cut-in cylinder group, an improved filling of the cylinders can be achieved if each cylinder in this group of cylinders is operated with two intake valves that have different valve lifts. With these different valve lifts per cylinder, a deliberate swirl can be produced. As a result of this deliberate swirl of the incoming fuel-air mixture or of the air drawn in, especially in the partial load range, the filling behavior and combustion process can be improved.
A valve drive of this kind is especially compact if the lift transfer element is designed as a tappet with two concentric lift elements. A valve drive of this kind can replace a conventional valve drive with tappets at a relatively small additional cost.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.